The DISTANCE Procedure

Proximity Measures

The following notation is used in this section:

v

the number of variables or the dimensionality

data for observation x and the jth variable, where

data for observation y and the jth variable, where

weight for the jth variable from the WEIGHTS= option in the VAR statement. when either or is missing.

W

the sum of total weights. No matter if the observation is missing or not, its weight is added to this metric.

mean for observation x

mean for observation y

the distance or dissimilarity between observations x and y

the similarity between observations x and y

The factor is used to adjust some of the proximity measures for missing values.

Methods That Accept All Measurement Levels

GOWER

Gower’s similarity

is computed as follows:

For nominal, ordinal, interval, or ratio variable,

For asymmetric nominal variable,

For nominal or asymmetric nominal variable,

For ordinal, interval, or ratio variable,

DGOWER

1 minus Gower

Methods That Accept Ratio, Interval, and Ordinal Variables

EUCLID

Euclidean distance

SQEUCLID

squared Euclidean distance

SIZE

size distance

SHAPE

shape distance

Note: squared shape distance plus squared size distance equals squared Euclidean distance.

COV

covariance similarity coefficient , where

CORR

correlation similarity coefficient

DCORR

correlation transformed to Euclidean distance as sqrt(1–CORR)

SQCORR

squared correlation

DSQCORR

squared correlation transformed to squared Euclidean distance as (1–SQCORR)

L(p)

Minkowski () distance, where p is a positive numeric value

CITYBLOCK

CHEBYCHEV

POWER(p,r)

generalized Euclidean distance, where p is a nonnegative numeric value and r is a positive numeric value. The distance between two observations is the rth root of sum of the absolute differences to the pth power between the values for the observations:

Methods That Accept Ratio Variables

SIMRATIO

similarity ratio

DISRATIO

one minus similarity ratio

NONMETRIC

Lance-Williams nonmetric coefficient

CANBERRA

Canberra metric coefficient. See Sneath and Sokal (1973, pp. 125–126)

COSINE

cosine coefficient

DOT

dot (inner) product coefficient

OVERLAP

sum of the minimum values

DOVERLAP

maximum of the sum of the x and the sum of y minus overlap

CHISQ

chi-square If the data represent the frequency counts, chi-square dissimilarity between two sets of frequencies can be computed. A 2-by-v contingency table is illustrated to explain how the chi-square dissimilarity is computed as follows:

	Variable				Row
Observation	Var 1	Var 2	…	Var v	Sum
X			…
Y			…
Column Sum			…		T

where

The chi-square measure is computed as follows:

where for j= 1, 2, …, v

CHI

square root of chi-square

PHISQ

phi-square This is the CHISQ dissimilarity normalized by the sum of weights

PHI

square root of phi-square

Methods That Accept Symmetric Nominal Variables

The following notation is used for computing to . Notice that only the nonmissing pairs are discussed below; all the pairs with at least one missing value will be excluded from any of the computations in the following section because

M

nonmissing matches

, where

X

nonmissing mismatches

, where

N

total nonmissing pairs

HAMMING: Hamming distance
MATCH: simple matching coefficient
DMATCH: simple matching coefficient transformed to Euclidean distance
DSQMATCH: simple matching coefficient transformed to squared Euclidean distance
HAMANN: Hamann coefficient
RT: Roger and Tanimoto
SS1: Sokal and Sneath 1
SS3: Sokal and Sneath 3. The coefficient between an observation and itself is always indeterminate (missing) since there is no mismatch.

The following notation is used for computing to . Notice that only the nonmissing pairs are discussed in the following section; all the pairs with at least one missing value are excluded from any of the computations in the following section because

Also, the observed nonmissing data of an asymmetric binary variable can have only two possible outcomes: presence or absence. Therefore, the notation, PX (present mismatches), always has a value of zero for an asymmetric binary variable.

The following methods distinguish between the presence and absence of attributes.

X

mismatches with at least one present

, where

PM

present matches

, where

PX

present mismatches

, where

PP

both present = PM + PX

P

at least one present = PM + X

PAX

present-absent mismatches

, where

N

total nonmissing pairs

Methods That Accept Asymmetric Nominal and Ratio Variables

JACCARD

Jaccard similarity coefficient

The JACCARD method is equivalent to the SIMRATIO method if there are only ratio variables; if there are both ratio and asymmetric nominal variables, the coefficient is computed as sum of the coefficient from the ratio variables (SIMRATIO) and the coefficient from the asymmetric nominal variables.

DJACCARD

Jaccard dissimilarity coefficient

The DJACCARD method is equivalent to the DISRATIO method if there are only ratio variables; if there are both ratio and asymmetric nominal variables, the coefficient is computed as sum of the coefficient from the ratio variables (DISRATIO) and the coefficient from the asymmetric nominal variables.

Methods That Accept Asymmetric Nominal Variables

DICE

Dice coefficient or Czekanowski/Sorensen similarity coefficient

RR

Russell and Rao. This is the binary equivalent of the dot product coefficient.

BLWNM | BRAYCURTIS

Binary Lance and Williams, also known as Bray and Curtis coefficient

K1

Kulcynski 1. The coefficient between an observation and itself is always indeterminate (missing) since there is no mismatch.